Establishment of new murine embryonic stem cell lines for the generation of mouse models of human genetic diseases

Impact of Reck expression and promoter activity in neuronal in vitro differentiation

Reck (REversion-inducing Cysteine-rich protein with Kazal motifs) tumor suppressor gene encodes a multifunctional glycoprotein which inhibits the activity of several matrix metalloproteinases (MMPs), and has the ability to modulate the Notch and canonical Wnt pathways. Reck-deficient neuro-progenitor cells undergo precocious differentiation; however, modulation of Reck expression during progression of the neuronal differentiation process is yet to be characterized. In the present study, we demonstrate that Reck expression levels are increased during in vitro neuronal differentiation of PC12 pheochromocytoma cells and P19 murine teratocarcinoma cells and characterize mouse Reck promoter activity during this process. Increased Reck promoter activity was found upon induction of differentiation in PC12 cells, in accordance with its increased mRNA expression levels in mouse in vitro models. Interestingly, Reck overexpression, prior to the beginning of the differentiation protocol, led to diminished efficiency of the neuronal differentiation process. Taken together, our findings suggest that increased Reck expression at early stages of differentiation diminishes the number of neuron-like cells, which are positive for the beta-3 tubulin marker. Our data highlight the importance of Reck expression evaluation to optimize in vitro neuronal differentiation protocols.

Functional properties of a Brazilian derived mouse embryonic stem cell line

Pluripotent mouse embryonic stem cells (mESC) are cell lines derived from the inner cell mass of blastocyst-stage early mammalian embryos. Since ion channel modulation has been reported to interfere with both growth and differentiation process in mouse and human ESC it is important to characterize the electrophysiological properties of newly generated mESC and compare them to other lines. In this work, we studied the intercellular communication by way of gap junctions in a Brazilian derived mESC (USP-1, generated by Dr. Lygia Pereira's group) and characterized its electrophysiological properties. We used immunofluorescence and RT-PCR to reveal the presence of connexin 43 (Cx43), pluripotency markers and ion channels. Using a co-culture of neonatal mouse cardiomyocytes with mESC, where the heart cells expressed the enhanced Green Fluorescent Protein, we performed dye injections to assess functional coupling between the two cell types observing dye diffusion. The patch-clamp study showed outward currents identified as two types of potassium currents, transient outward potassium current (Ito) and delayed rectifier outward potassium current (Iks), by use of specific drug blockage. Calcium or sodium currents in undifferentiated mESC were not identified. We conclude that USP-1 mESC has functional Cx43 channels establishing intercellular communication among themselves and with cardiomyocytes and has a similar electrophysiological profile compared to other mESC cell lines.

Conserved transcription factor binding sites suggest an activator basal promoter and a distal inhibitor in the galanin gene promoter in mouse ES cells

Galanin and its receptors have been shown to be expressed in undifferentiated mouse embryonic stem (ES) cells through transcriptome and proteomic analyses. Although transcriptional regulation of galanin has been extensively studied, the regulatory proteins that mediate galanin expression in mouse ES cells have not yet been determined. Through sequence alignments, we have found a high degree of similarity between mouse and human galanin upstream sequences at -146 bp/+69 bp (proximal region) and -2,408 bp/-2,186 bp (distal region). These regions could be recognized by ES cell nuclear proteins, and EMSA analysis suggests a specific functionality. Analysis of the proximal region (PR) using EMSA and ChIP assays showed that the CREB protein interacts with the galanin promoter both in vitro and in vivo. Additional EMSA analysis revealed that an SP1 consensus site mediated protein-DNA complex formation. Reporter assays showed that CREB is an activator of galanin expression and works cooperatively with SP1. Furthermore, analysis of the distal region (DR) using EMSA assays demonstrated that both HOX-F and PAX 4/6 consensus sites mediated protein-DNA complex formation, and both sites inhibited luciferase activity in reporter assays. These data together suggest that CRE and SP1 act as activators at the basal promoter, while HOX-F and PAX 4/6 act as silencers of transcription. The interplay of these transcription factors (TF) may drive regulated galanin expression in mouse ES cells.

VP22 herpes simplex virus protein can transduce proteins into stem cells

The type I herpes simplex virus VP22 tegument protein is abundant and well known for its ability to translocate proteins from one cell to the other. In spite of some reports questioning its ability to translocate proteins by attributing the results observed to fixation artifacts or simple attachment to the cell membrane, VP22 has been used to deliver several proteins into different cell types, triggering the expected cell response. However, the question of the ability of VP22 to enter stem cells has not been addressed. We investigated whether VP22 could be used as a tool to be applied in stem cell research and differentiation due to its capacity to internalize other proteins without altering the cell genome. We generated a VP22.eGFP construct to evaluate whether VP22 could be internalized and carry another protein with it into two different types of stem cells, namely adult human dental pulp stem cells and mouse embryonic stem cells. We generated a VP22.eGFP fusion protein and demonstrated that, in fact, it enters stem cells. Therefore, this system may be used as a tool to deliver various proteins into stem cells, allowing stem cell research, differentiation and the generation of induced pluripotent stem cells in the absence of genome alterations.

Equivalency of buffalo (Bubalus bubalis) embryonic stem cells derived from fertilized, parthenogenetic, and hand-made cloned embryos

This study was aimed at establishing buffalo embryonic stem cells (ESCs) from in vitro fertilized (IVF), parthenogenetic, and hand-made cloned (HMC) embryos and to check their equivalency in terms of stem cell marker expression, longevity, proliferation, and differentiation pattern. ESCs derived from all three sources were found by immunofluorescence to express the pluripotency markers SSEA-4, TRA-1-60, TRA-1-81, OCT4, and SOX2 and were able to form embryoid bodies containing cells expressing genes specific to endoderm (AFP, HNF4, and GATA4), mesoderm (MSX1, BMP4, and ASA), and ectoderm (cytokeratin 8 and NF68). Reverse transcriptase PCR (RT-PCR) showed cells from all sources to be positive for pluripotency markers OCT4, SOX2, NANOG, STAT3, REX1, FOXD3, NUCLEOSTEMIN, and TELOMERASE. Pluripotency markers OCT4, SOX2, NANOG, and c-MYC were also analyzed by real-time PCR. No significant differences were observed among ESCs from all three sources for all these genes except NANOG, whose expression was higher (p<0.05) in HMC-derived ESCs (6.897±2.3) compared to that in parthenogenesis- and IVF-derived cells (1.603±0.315 and 1±0, respectively). Pluripotent, stable buffalo ESC lines derived from IVF, parthenogenesis, and HMC embryos may be genetically manipulated to provide a powerful tool for studies involving embryonic development, genomic imprinting, gene targeting, cloning, chimera formation, and transgenic animal production.

Dynamic expression of synemin isoforms in mouse embryonic stem cells and neural derivatives

Background

Intermediate filaments (IFs) are major components of the mammalian cytoskeleton and expressed in cell-type-specific patterns. Morphological changes during cell differentiation are linked to IF network remodeling. However, little is known concerning the presence and the role of IFs in embryonic stem (ES) cells and during their differentiation.

Results

We have examined the expression profile of synemin isoforms in mouse pluripotent ES cells and during their neural differentiation induced by retinoic acid. Using RT-PCR, Western blotting and immunostaining, we show that synemin M is present at both mRNA and protein levels in undifferentiated ES cells as early as pluripotency factor Oct-3/4 and IF keratin 8. Synemin H was produced only in neural precursors when neural differentiation started, concurrently with synemin M, nestin and glial fibrillary acidic protein. However, both synemin H and M were restricted to the progenitor line during the neural differentiation program. Our in vivo analysis also confirmed the expression of synemins H/M in multipotent neural stem cells in the subventricular zone of the adult brain, a neurogenic germinal niche of the mice. Knocking down synemin in ES cells by shRNA lentiviral particles transduction has no influence on expression of Oct4, Nanog and SOX2, but decreased keratin 8 expression.

Conclusions

Our study shows a developmental stage specific regulation of synemin isoforms in ES cells and its neural derivatives. These findings represent the first evidence that synemins could potentially be useful markers for distinguishing multipotent ES cells from undifferentiated neural stem cells and more committed progenitor cells.

Molecular analysis of the differentiation potential of murine mesenchymal stem cells from tissues of endodermal or mesodermal origin

Mesenchymal stem cells (MSCs) have received great attention due to their remarkable regenerative, angiogenic, antiapoptotic, and immunosuppressive properties. Although conventionally isolated from the bone marrow, they are known to exist in all tissues and organs, raising the question on whether they are identical cell populations or have important differences at the molecular level. To better understand the relationship between MSCs residing in different tissues, we analyzed the expression of genes related to pluripotency (SOX2 and OCT-4) and to adipogenic (C/EBP and ADIPOR1), osteogenic (OMD and ALP), and chondrogenic (COL10A1 and TRPV4) differentiation in cultures derived from murine endodermal (lung) and mesodermal (adipose) tissue maintained in different conditions. MSCs were isolated from lungs (L-MSCs) and inguinal adipose tissue (A-MSCs) and cultured in normal conditions, in overconfluence or in inductive medium for osteogenic, adipogenic, or chondrogenic differentiation. Cultures were characterized for morphology, immunophenotype, and by quantitative real-time reverse transcription-polymerase chain reaction for expression of pluripotency genes or markers of differentiation. Bone marrow-derived MSCs were also analyzed for comparison of these parameters. L-MSCs and A-MSCs exhibited the typical morphology, immunophenotype, and proliferation and differentiation pattern of MSCs. The analysis of gene expression showed a higher potential of adipose tissue-derived MSCs toward the osteogenic pathway and of lung-derived MSCs to chondrogenic differentiation, representing an important contribution for the definition of the type of cell to be used in clinical trials of cell therapy and tissue engineering.

Cysteine proteases in differentiation of embryonic stem cells into neural cells

Glycosylated mouse cystatin C (mCysC), an endogenous inhibitor of cysteine cathepsin proteases (CP), has been suggested as a cofactor of β-FGF to induce the differentiation of mouse embryonic stem cells into neural progenitor cells (NPCs). To investigate the possible role of CP in neural differentiation, we treated embryoid bodies (EBs) with (i) E64, an inhibitor of papain-like CP and of calpains, (ii) an inhibitor of cathepsin L (iCatL), (iii) an inhibitor of calpains (iCalp), or (iv) cystatins, and their ability to differentiate into neural cells was assessed. We show that the inhibition of CP induces a significant increase in Pax6 expression in EBs, leading to an increase in the number of nestin-positive cells after 3 days. Fourteen days after E64 treatment, we observed increased numbers of β-III-tubulin-positive cells, showing greater percentage of immature neurons, and this feature persisted up to 24 days. At this point, we encountered higher numbers of neurons with inward Na(+) current compared with untreated EBs. Further, we show that mCysC and iCatL, but not unglycosylated egg white cystatin or iCalp, increased the numbers of NPCs. In contrast to E64 and iCatL, mCysC did not inhibit CP in EBs and its neural-inducing activity required β-FGF. We propose that the inhibition of CP induces the differentiation of mouse embryonic stem cells into NPCs and neurons through a mechanism that is distinct from CysC-induced neural differentiation.

Mesenchymal and embryonic characteristics of stem cells obtained from mouse dental pulp

OBJECTIVE

Several studies have demonstrated that human dental pulp is a source of mesenchymal stem cells. To better understand the biological properties of these cells we isolated and characterized stem cells from the dental pulp of EGFP transgenic mice.

METHODS

The pulp tissue was gently separated from the roots of teeth extracted from C57BL/6 mice, and cultured under appropriate conditions. Flow cytometry, RT-PCR, light microscopy (staining for alkaline phosphatase) and immunofluorescence were used to investigate the expression of stem cell markers. The presence of chromosomal abnormalities was evaluated by G banding.

RESULTS

The mouse dental pulp stem cells (mDPSC) were highly proliferative, plastic-adherent, and exhibited a polymorphic morphology predominantly with stellate or fusiform shapes. The presence of cell clusters was observed in cultures of mDPSC. Some cells were positive for alkaline phosphatase. The karyotype was normal until the 5th passage. The Pou5f1/Oct-4 and ZFP42/Rex-1, but not Nanog transcripts were detected in mDPSC. Flow cytometry and fluorescence analyses revealed the presence of a heterogeneous population positive for embryonic and mesenchymal cell markers. Adipogenic, chondrogenic and osteogenic differentiation was achieved after two weeks of cell culture under chemically defined in vitro conditions. In addition, some elongated cells spontaneously acquired a contraction capacity.

CONCLUSIONS

Our results reinforce that the dental pulp is an important source of adult stem cells and encourage studies on therapeutic potential of mDPSC in experimental disease models.

A new mouse model for marfan syndrome presents phenotypic variability associated with the genetic background and overall levels of Fbn1 expression

Marfan syndrome is an autosomal dominant disease of connective tissue caused by mutations in the fibrillin-1 encoding gene FBN1. Patients present cardiovascular, ocular and skeletal manifestations, and although being fully penetrant, MFS is characterized by a wide clinical variability both within and between families. Here we describe a new mouse model of MFS that recapitulates the clinical heterogeneity of the syndrome in humans. Heterozygotes for the mutant Fbn1 allele mgΔ^loxPneo, carrying the same internal deletion of exons 19–24 as the mgΔ mouse model, present defective microfibrillar deposition, emphysema, deterioration of aortic wall and kyphosis. However, the onset of a clinical phenotypes is earlier in the 129/Sv than in C57BL/6 background, indicating the existence of genetic modifiers of MFS between these two mouse strains. In addition, we characterized a wide clinical variability within the 129/Sv congenic heterozygotes, suggesting involvement of epigenetic factors in disease severity. Finally, we show a strong negative correlation between overall levels of Fbn1 expression and the severity of the phenotypes, corroborating the suggested protective role of normal fibrillin-1 in MFS pathogenesis, and supporting the development of therapies based on increasing Fbn1 expression.

Phosphoproteomics profiling suggests a role for nuclear βΙPKC in transcription processes of undifferentiated murine embryonic stem cells

Protein kinase C (PKC) plays a key role in embryonic stem cell (ESC) proliferation, self-renewal, and differentiation. However, the function of specific PKC isoenzymes have yet to be determined. Of the PKCs expressed in undifferentiated ESCs, βIPKC was the only isoenzyme abundantly expressed in the nuclei. To investigate the role of βΙPKC in these cells, we employed a phosphoproteomics strategy and used two classical (cPKC) peptide modulators and one βIPKC-specific inhibitor peptide. We identified 13 nuclear proteins that are direct or indirect βΙPKC substrates in undifferentiated ESCs. These proteins are known to be involved in regulating transcription, splicing, and chromatin remodeling during proliferation and differentiation. Inhibiting βΙPKC had no effect on DNA synthesis in undifferentiated ESCs. However, upon differentiation, many cells seized to express βΙPKC and βΙPKC was frequently found in the cytoplasm. Taken together, our results suggest that βIPKC takes part in the processes that maintain ESCs in their undifferentiated state.

Maintenance of pluripotency in mouse embryonic stem cells cultivated in stirred microcarrier cultures

The development of efficient and reproducible culture systems for embryonic stem (ES) cells is an essential pre-requisite for regenerative medicine. Culture scale-up ensuring maintenance of cell pluripotency is a central issue, because large amounts of pluripotent cells must be generated to warrant that differentiated cells deriving thereof are transplanted in great amounts and survive the procedure. This study aimed to develop a robust scalable cell expansion system, using a murine embryonic stem cell line that is feeder-dependent and adapted to serum-free medium, thus representing a more realistic model for human ES cells. We showed that high concentrations of murine ES cells can be obtained in stirred microcarrier-based spinner cultures, with a 10-fold concentration of cells per volume of medium and a 5-fold greater cell concentration per surface area, as compared to static cultures. No differences in terms of pluripotency and differentiation capability were observed between cells grown in traditional static systems and cells that were replated onto the traditional system after being expanded on microcarriers in the stirred system. This was verified by morphological analyses, quantification of cells expressing important pluripotency markers (Oct-4, SSEA-1, and SOX2), karyotype profile, and the ability to form embryoid bodies with similar sizes, and maintaining their intrinsic ability to differentiate into all three germ layers.

Long-term culture of mouse embryonic stem cell-derived adherent neurospheres and functional neurons

Innumerous protocols, using the mouse embryonic stem (ES) cells as model for in vitro study of neurons functional properties and features, have been developed. Most of these protocols are short lasting, which, therefore, does not allow a careful analysis of the neurons maturation, aging, and death processes. We describe here a novel and efficient long-lasting protocol for in vitro ES cells differentiation into neuronal cells. It consists of obtaining embryoid bodies, followed by induction of neuronal differentiation with retinoic acid of nonadherent embryoid bodies (three-dimensional model), which further allows their adherence and formation of adherent neurospheres (AN, bi-dimensional model). The AN can be maintained for at least 12 weeks in culture under repetitive mechanical splitting, providing a constant microenvironment (in vitro niche) for the neuronal progenitor cells avoiding mechanical dissociation of AN. The expression of neuron-specific proteins, such as nestin, sox1, beta III-tubulin, microtubule-associated protein 2, neurofilament medium protein, Tau, neuronal nuclei marker, gamma-aminobutyric acid, and 5-hydroxytryptamine, were confirmed in these cells maintained during 3 months under several splitting. Additionally, expression pattern of microtubule-associated proteins, such as lissencephaly (Lis1) and nuclear distribution element-like (Ndel1), which were shown to be essential for differentiation and migration of neurons during embryogenesis, was also studied. As expected, both proteins were expressed in undifferentiated ES cells, AN, and nonrosette neurons, although presenting different spatial distribution in AN. In contrast to previous studies, using cultured neuronal cells derived from embryonic and adult tissues, only Ndel1 expression was observed in the centrosome region of early neuroblasts from AN. Mature neurons, obtained from ES cells in this work, display ionic channels and oscillations of membrane electrical potential typical of electrically excitable cells, which is a characteristic feature of the functional central nervous system (CNS) neurons. Taken together, our study demonstrated that AN are a long-term culture of neuronal cells that can be used to analyze the process of neuronal differentiation dynamics. Thus, the protocol described here provides a new experimental model for studying neurological diseases associated with neuronal differentiation during early development, as well as it represents a novel source of functional cells that can be used as tools for testing the effects of toxins and/or drugs on neuronal cells.

Generation of mouse embryonic stem cell lines from zona-free nuclear transfer embryos

Pluripotent stem cells would have great potential in cell therapies and drug development when genetically matched with the patient; thus, histocompatible cells could be used in transplantation therapy or as a source of patient-specific cells for drug testing. Pluripotent embryonic stem cells (ESCs)-generated via somatic cell nuclear transfer (SCNT) or parthenogenesis (pESC)-are potential sources of histocompatible cells and tissues for transplantation. Earlier studies used the piezoelectric microinjection (PEM) technique for nuclear transfer (NT) in mouse. No specific studies examined zona-free (ZF) NT as an alternative NT method to generate genetically matched ESCs of a nuclear donor. In this study, we compared the efficiency of nuclear transfer-derived ESC (ntESC) line establishment from ZF-NT, ZF-parthenogenetic (PGA), and ZF-fertilized embryos with that of the PEM-NT method. Different nuclei donor cells [cumulus, ESC, and mouse embryonic fibroblast (MEF)] were used and the efficiency of ntESC derivation was investigated, along with their in vitro characterization. The ZF-NT method's efficiency was higher than that of the PEM-NT using cumulus cells. When ESCs and cumulus cells were used as nuclear donor cells, they resulted in significantly higher ZF-NT-derived ntESC line establishment rates compared to MEF cells. In conclusion, the nuclear donor cell type significantly affected the efficiency of ntESC line establishment, and the ZF-NT method was efficient to establish pluripotent ntESC lines.

Development of single mouse blastomeres into blastocysts, outgrowths and the establishment of embryonic stem cells

The recently developed technique of establishing embryonic stem (ES) cell lines from single blastomeres (BTMs) of early mouse and human embryos has created significant interest in this source of ES cells. However, sister BTMs of an early embryo might not have equal competence for the development of different lineages or the derivation of ES cells. Therefore, single BTMs from two- and four-cell embryos of outbred mice were individually placed in sequential cultures to enhance the formation of the inner cell mass (ICM) and the establishment of embryonic outgrowth. The outgrowths were then used for the derivation of ES cell lines. Based on the expression of ICM (Sox2) and trophectoderm (Cdx2) markers, it was determined that ICM marker was lacking in blastocysts derived from 12% of BTMs from two-cell stage and 20% from four-cell stage. Four ES cell lines (5.6%; 4/72) were established ater culture of single BTMs from two-cell embryos, and their pluripotency was demonstrated by their differentiation into neuronal cell types. Our results demonstrate that sister BTMs of an early embryo are not equally competent for ICM marker expression. However, we demonstrated the feasibility of establishing ES cells from a single BTM of outbred mice.

Crotamine mediates gene delivery into cells through the binding to heparan sulfate proteoglycans

Recently we have shown that crotamine, a toxin from the South American rattlesnake Crotalus durissus terrificus venom, belongs to the family of cell-penetrating peptides. Moreover, crotamine was demonstrated to be a marker of centrioles, of cell cycle, and of actively proliferating cells. Herein we show that this toxin at non-toxic concentrations is also capable of binding electrostatically to plasmid DNA forming DNA-peptide complexes whose stabilities overcome the need for chemical conjugation for carrying nucleic acids into cells. Interestingly, crotamine demonstrates cell specificity and targeted delivery of plasmid DNA into actively proliferating cells both in vitro and in vivo, which distinguishes crotamine from other known natural cell-penetrating peptides. The mechanism of crotamine penetration and cargo delivery into cells was also investigated, showing the involvement of heparan sulfate proteoglycans in the uptake phase, which is followed by endocytosis and peptide accumulation within the acidic endosomal vesicles. Finally, the permeabilization of endosomal membranes induced by crotamine results in the leakage of the vesicles contents to the cell cytosol.

Genetic basis of human testicular germ cell cancer: insights from the fruitfly and mouse

The prevalence of tumours of the germ line is increasing in the male population. This complex disease has a complex aetiology. We examine the contribution of genetic mutations to the development of germ line tumours in this review. In particular, we concentrate on fly and mouse experimental systems in order to demonstrate that mutations in some conserved genes cause pathologies typical of certain human germ cell tumours, whereas other mutations elicit phenotypes that are unique to the experimental model. Despite these experimental systems being imperfect, we show that they are useful models of human testicular germ cell tumourigenesis.

Crotamine is a novel cell-penetrating protein from the venom of rattlesnake Crotalus durissus terrificus

Herein we report that crotamine, a small lysine- and cysteine-rich protein from the venom of the South American rattlesnake, can rapidly penetrate into different cell types and mouse blastocysts in vitro. In vivo crotamine strongly labels cells from mouse bone marrow and spleen and from peritoneal liquid, as shown by fluorescent confocal laser-scanning microscopy. Nuclear localization of crotamine was observed in both fixed and unfixed cells. In the cytoplasm, crotamine specifically associates with centrosomes and thus allows us to follow the process of centriole duplication and separation. In the nucleus, it binds to the chromosomes at S/G2 phase, when centrioles start dividing. Moreover, crotamine appears as a marker of actively proliferating cells, as shown by 5-BrdU cell-proliferation assay. Crotamine in the micromolar range proved nontoxic to any of the cell cultures tested and did not affect the pluripotency of ES cells or the development of mouse embryos.